The present invention relates to an apparatus and a method for attaching conductive balls forming bumps onto a substrate.
Concerning the method for forming electrodes on a substrate on which electronic parts are mounted, a method of using conductive balls is known. According to this method, after conductive balls such as solder balls have been attached onto electrodes on a substrate, the conductive balls are heated, so that bumps (protruding electrodes) are formed on the electrodes on the substrate.
Concerning the method for attaching the conductive balls onto the electrodes on the substrate, a method of using a suction head is known. According to this method, the conductive balls are vacuum-absorbed and held onto a lower surface of the suction head and attached onto the electrodes on the substrate. This method is advantageous in that a large number of conductive balls can be effectively attached onto a large number of electrodes all at once.
In the case where the conductive balls are attached onto the substrate by the suction head, it is necessary to accurately position the conductive balls to the electrodes on the substrate. Therefore, before the conductive balls are attached onto the substrate, positional recognition of the substrate is required. Conventionally, in the suction head, there is provided one set of camera used for positional recognition of the substrate. While the camera used for positional recognition is moved in the horizontal direction integrally with the suction head, positional recognition marks formed on an upper surface of the substrate are observed by the camera.
There are provided two positional recognition marks on the substrate. In order to enhance the positional recognition accuracy of the substrate, these positional recognition marks are formed at two positions on a diagonal line of the substrate, and a distance between the two positional recognition marks is extended as long as possible. Accordingly, when the conventional apparatus is used, the camera must be horizontally moved by a long distance and these two positional recognition marks must be successively observed by the camera. Therefore, the tact time required for the positional recognition of the substrate is extended, and the productivity can not be enhanced.
Especially, positional recognition of the substrate must be conducted individually for a large number of substrates. Since the size of the substrate is increased recently and a distance between the two positional recognition marks is increased, the tact time is extended for the positional recognition of the substrate, and it becomes impossible to enhance the productivity.